1. Field of the Invention
The present invention relates to a method of manufacturing a field-effect transistor, a field-effect transistor, a display device and an electromagnetic wave detector.
2. Description of the Related Art
In recent years, with the progress of the liquid crystal and electroluminescence (EL) technologies and the like, flat panel display devices (FPD) are put into practical use. In particular, since high bright-light emission at low voltage can be achieved by using organic electroluminescent devices (hereinafter, may be recited as “organic EL devices”) using a thin film material which is excited by applying electric current thereto, it is expected that thinning, weight saving, downsizing and electric power saving of devices in a wide range of areas including mobile phone displays, personal digital assistants (PDA), computer displays, automobile information displays, TV monitor displays and generic illumination are realized. Further, these FPDs are driven by an active matrix circuit of a field-effect transistor (hereinafter, may be referred to as a TFT) in which an amorphous silicon thin film or a polycrystalline silicon thin layer formed on a glass substrate is used for an oxide semiconductor layer.
On the other hand, attempts to use a lightweight and flexible resin substrate in place of the glass substrate of FPD have been made for improving the thinning, weight saving and resistance to breakage. However, the manufacture of transistors using the silicon thin film requires a heating process at a relatively high temperature, so that in general, it is difficult to form the silicon thin film directly on a resin substrate with low heat-resistance. Accordingly, development of TFTs using oxide semiconductors capable of forming a film at low temperature is now actively being carried out. The oxide semiconductor is capable of film-forming at room temperature, and being formed on a film, thereby attracting the attention as a material of the oxide semiconductors. Further, in such a TFT, for the purpose of protecting and electrically insulation-separating an oxide semiconductor layer or a electroconductive layer including a source electrode and a drain electrode provided in the TFT, an insulation layer so as to cover the areas corresponding to the oxide semiconductor layer or the conductive layer is generally provided. As a layer equivalent to the insulation layer having such a function, the use of silicon oxide is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2007-73705.
Here, the TFT is suitably applied to electromagnetic wave detectors which detect electromagnetic waves such as X-rays, or displays using a liquid crystal element and an organic EL (electroluminescence) element. When the TFT is applied to various devices such as these electromagnetic wave detectors, display elements or the like, it is necessary to connect electrically a part of the electroconductive layer to the elements provided in these various devices. Accordingly, when the TFT is applied to these various devices, the insulation layer formed on the electroconductive layer is processed to form a contact hole, so that a part of the electroconductive layer is exposed, and the electroconductive layer is electrically connected to the various devices via the exposed area.
However, since the silicon oxide (SiO2) recited in JP-A No. 2007-73705 as a constituent material for the insulation layer has an alkali resistance as well as an acid resistance, it is necessary to select a processing by dry-etching, resulting in a problem of an increase in production cost.
Moreover, in JP-A No. 2007-73705, although an embodiment in which materials other than silicon oxide are used is disclosed, since the processing is carried out by an argon milling method, there is a problem with the processing such that the surface of the insulation layer is susceptible to damage at the time of the processing of the insulation layer. Further, a method of the use of a strong acidic solution for processing the insulation layer is conceivable, but this method may be problematic because of the occurrence of erosion of the insulation layer.